LeetCode Solutions/Binary Search Study Plan/Binary Search I/Peak Index in a Mountain Array.java
class Solution {
    public int peakIndexInMountainArray(int[] arr) {
        int left = 0, right = arr.length - 1;
        while (left < right){
            int mid = (left + right) / 2;            
            if (arr[mid] < arr[mid + 1]){
                left = mid + 1;
            }
            else{
                right = mid;
            }
        }
        return left;
    }
}